Calculating hours only relevant hours to a category

Hi Community, I can get my code to sum total annual leave when string includes "AL" however, if the string include another category e.g. "SK" for sick leave, I get NaN sum value error. I need help to make my JavaScript to only see strings value associated with AL and then calculate over 5 days e.g vars A to E.
I may be going about this the completely wrong way.. any help would be appreciated. Thanks

//sum annual leave over working week

//Mon to Fri var's a to e

var a = getField("CHset1").valueAsString;
var b = getField("CHset2").valueAsString;
var c = getField("CHset3").valueAsString;
var d = getField("CHset4").valueAsString;
var e = getField("CHset5").valueAsString;

event.value="";

var parts1 = a.split("AL, ");
var parts2 = b.split("AL, ");
var parts3 = c.split("AL, ");
var parts4 = d.split("AL, ");
var parts5 = e.split("AL, ");

if (parts.length >=2)
{
event.value = (1*parts1[1]) + (1*parts2[1]) + (1*parts3[1]) + (1*parts4[1]) + (1*parts5[1]);
}
else event.value = "";